The present invention relates to a semiconductor fabricating apparatus for producing a semiconductor device by depositing a thin film on a silicon wafer or by subjecting the latter to an impurity diffusion treatment, etc., to a method for modifying the positional displacement of a wafer in a wafercassette within the semiconductor fabricating apparatus, and to a method for transferring the wafer cassette.
Referring to FIGS. 9 and 10, a conventional semiconductor fabricating apparatus will now be described.
The apparatus includes a housing 1 in which a cassette transfer unit 2 is provided at a front side thereof for achieving the transfer of a wafer cassette 11 between the apparatus and an external transfer system. Behind the cassette transfer unit 2, there is provided a cassette transfer device 3. Provided behind the cassette transfer device 3 is a cassette storage 4. A buffer storage 5 is disposed upwardly of the cassette storage 4. Behind the buffer storage 5, there is provided a clean unit 6. Disposed at a rear upper part of the housing 1 is a vertical reaction furnace 7. Below the reaction furnace 7, there is provided a boat elevator 9 for introducing into and withdrawing from the furnace 7 a boat 8. Between the boat elevator 9 and the cassette storage 4, there is provided a wafer transfer device 10. Reference numeral 25 designates a clean unit.
The cassette transfer device 3 is supported on a drive portion 24 which can move upward, downward and in a horizontal direction. The cassette transfer device 3 includes a cassette loader 13 which is designed to rotate about a horizontal axial center 15 by approximately 90.degree.. The cassette loader 13 also includes a cassette transfer plate 16 capable of back and forth movements and a cassette receiver 17 disposed perpendicularly to the cassette transfer plate 16.
Each of the cassette storage 4 and the buffer storage 5 has plural rows of cassette shelves (three rows of three shelves shown in the figures) . The number of the shelves is at least greater than the number of wafer cassettes required for single batch processing.
The wafer transfer device 10 comprises a rotary stage 18 which can move upward and downward and rotate and a wafer chuck 19 capable of advancing and retracting movements mounted on the rotary stage 18. The wafer chuck 19 includes plural chuck plates 20 arranged vertically.
The boat elevator 9 includes a boat receiver plate 21 which can move upward and downward for supporting the boat 8 thereon.
The reaction furnace 7 is comprised of a cylindrical heater 22 and a reaction tube 23 located internally of the heater 22 and forming a reaction chamber which is sealingly closed by the full insertion of the boat 8.
The wafer cassette 11 loading wafers 12 is transferred from the external transfer system to the cassette transfer unit 2 in an upwardly-oriented position. Then, the transferred wafer cassette 11 is held by the cassette transfer device 3 and transferred from the cassette transfer unit 2 to the cassette storage 4 after it is rotated by 90.degree. to be brought to a horizontal position.
The wafer transfer device 10 effects the transfer of the wafers 12 between the cassette storage 4 and the boat 8.
By the upward and downward movements and rotation of the rotary stage 18, the wafer chuck 19 is brought to oppose the wafer cassette 11 to be transferred. Then, by the forward and backward movements of the wafer chuck 19, the wafers 12 are chucked by the chuck plate 20. Thereafter, the chucked wafers 12 are sequentially loaded onto the boat 8 through the upward and downward movements and rotation of the rotary stage 18 and the forward and backward movements of the wafer chuck 19. Within a predetermined range at the upper and lower portions of the boat 8, there are provided dummy wafers as well as monitor wafers at predetermined intervals.
When the loading of the wafers onto the boat 8 is completed, the boat elevator 9 introduces the boat 8 into the reaction furnace 7 for treatment of the wafers.
The treated wafers are loaded back onto the wafer cassette backwardly following the wafer cassette transfer procedure described above, whereafter the wafer cassette is taken out again following backwardly the wafer cassette transfer procedure. The dummy wafers are used repeatedly. Thus, no transfer operations are conducted with respect to the dummy wafers when the semiconductor fabricating apparatus is in operation.
In the described conventional semiconductor fabricating apparatus, the cassette storage 4 and the buffer storage 5 are both arranged to accommodate the wafer cassettes 11 in horizontally-oriented positions.
Further, as described above, the dummy wafers are used repeatedly within the semiconductor fabricating apparatus and thus undergo repeated transfer operations between the boat 8 and the wafer cassettes in the cassette storage 4. As a result, it is likely that the dummy wafers are positionally displaced with respect to the wafer cassette 11 due to transfer errors and vibrations to occur during transfer of the wafers 12. Such positional displacement of the dummy wafers may accumulates and exceed the tolerable level.
If such positional displacement of the wafers exceeds the tolerable level, such troubles as impossibility of wafer transfer, damaging of the wafers and down-fall of the boat may result. This may further lead to the stoppage of the apparatus, thus lowering the serviceability ratio of the apparatus. Apart from this, since cleanliness within the semiconductor fabricating apparatus significantly affects the treatment quality of the wafers, improved cleanliness within the apparatus has been desired.